Set Appliance State:
Mains Power Off
Set Multimeter to Resistance 
Isolate Mains Power to appliance as per TOPs P4
Measurement:
Disconnect the Burner Flame Sense Electrode
Lead (1) from the Sense Electrode and measure
the Lead continuity between the disconnected Lead
and connection 8 (Grey wire, marked FLAME P) on
the PCB connector multiplug.
Lead (1) from the Sense Electrode and measure
the Lead continuity between the disconnected Lead
and connection 8 (Grey wire, marked FLAME P) on
the PCB connector multiplug.
Isolate as per TOPs P4
and refit as necessary